staging:iio:ad7606: Run trigger handler only once per trigger event

Currently the ad7606 driver installs the same function for the hard-irq and
threaded trigger handlers. This was introduced in commit 1caf7cb46135
("staging:iio:adc:ad7606 Convert to new channel registration method Update
Add missing call to iio_trigger_notify_done() Set pollfunc top and bottom
half handler"). Unfortunately the commit message does not mention why this
was done and Michael does not remember either.

Since the trigger handler function is idempotent (set a GPIO to 1) running
it twice does not do any harm, but is simply not necessary either. So set
the threaded trigger handler for the driver to NULL.

While we are at it also remove the function description comment that does
no say anything that can't be derived from the function name itself.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7606_ring.c

@@ -18,11 +18,7 @@
 
 #include "ad7606.h"
 
-/**
- * ad7606_trigger_handler_th() th/bh of trigger launched polling to ring buffer
- *
- **/
-static irqreturn_t ad7606_trigger_handler_th_bh(int irq, void *p)
+static irqreturn_t ad7606_trigger_handler(int irq, void *p)
 {
 	struct iio_poll_func *pf = p;
 	struct ad7606_state *st = iio_priv(pf->indio_dev);
@@ -63,9 +59,8 @@ int ad7606_register_ring_funcs_and_init(struct iio_dev *indio_dev)
 
 	INIT_WORK(&st->poll_work, &ad7606_poll_bh_to_ring);
 
-	return iio_triggered_buffer_setup(indio_dev,
-		&ad7606_trigger_handler_th_bh, &ad7606_trigger_handler_th_bh,
-		NULL);
+	return iio_triggered_buffer_setup(indio_dev, &ad7606_trigger_handler,
+					  NULL, NULL);
 }
 
 void ad7606_ring_cleanup(struct iio_dev *indio_dev)